364 AXNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



is heated to about 3,000° C., it reaches the water cooler, where its 

 temperature is then suddenly reduced. At this point there is a rapid 

 mixing of the highly heated nitric oxide next to the arc, with the 

 cooler air that is whirling past, and the gas becomes permanently 

 fixed. The nitric oxide and air leave the top of the cooler at about 

 1,200° C, and pass away to a gas flue, common to all the furnaces, 

 where the temperature is reduced to about 850° C. 



The plant at Christiansand is entirely occupied in making sodium 

 nitrite for the production of aniline dyes, etc. Previously sodium 

 nitrite had been made by the reduction of Chile nitrate with lead, 

 but this method of production has now practically ceased. 



The nitrite made from the nitrogen of the air is so satisfactory 

 and so cheap, compared with the old methods, that now practically the 

 whole supply of the world, valued at £160,000 ($800,000), is obtained 

 by electricity. 



In order to produce it the temperature of the gases is not allowed 

 to fall below 300° C., and this keeps the nitric oxide about equal 

 to the nitrogen peroxide. This mixture behaves as if it were nitrogen 

 trioxide NoO,, and it is absorbed completely by being brought into 

 contact with sodium hydroxide according to the followiiig formula — 



NO+NO,+2NaOH=H20+2NaNO (sodium nitrite). 



CALCIUM NITRATE. 



As carried out at Notodden, the method of making calcium nitrate 

 is as follows: The nitric oxide gas and air pass from each furnace 

 into two fireproof -lined gas-collecting pipes, about 6 feet in diameter, 

 lined with fire brick. These pipes convey the gas to four steam 

 boilers, the heat given off by the gases being used to raise steam for 

 concentrating the products and for driving the air compressors for 

 pumping acids, soda, etc. The gases then go through tubes in the 

 evaporating tanks, after which the temperature is down to about 

 250° C. The temperature is lowered still further, to 50° C, by 

 passing it through a number of aluminium tubes over which cold 

 water is flowing. The gas then enters the oxidation tanks, which are 

 large vertical iron cylinders, having acid-proof linings. Here it 

 continues to take up oxygen to form nitrogen peroxide, the per- 

 centages being now about 98 per cent air and 2 per cent nitrogen 

 peroxide. 



The nitrogen peroxide is brought into contact with water to form 

 nitric acid, in two series of four towers. These towers are built of 

 granite and are filled with broken quartz, this substance and the 

 granite being chosen because they are not affected by acids. Each 

 tower measures 2 meters square by 10 meters high, and it has been 

 found that they will give an absorption of 3.3 kilograms of nitric 

 acid per cubic meter of space per 24 hours. 



